FX4 isn't a trim level on the 2011-2012. It's just an accessory package.

Includes:
All-Terrain tires
Rancho branded shocks(Ford shocks painted White with a Rancho Sticker)
Transfer Case and Fuel Tank Skid Plates
Hill Descent Control

It requires that you get a Limited Slip axle on the DRW trucks and an Electronic Locking axle on the SRW trucks. Also requires 4x4.

You can get the FX4 package on any trim level(XL/XLT/Lariat/KIng Ranch).